1. Field of the Invention
The present invention relates to oil change interval monitors generally, and more particularly to a device which monitors the useful life of engine oil during the normal operation of a diesel engine and provides an indication to the engine operator of the optimal time to change the engine oil. The oil change interval monitor is especially useful with trucks and recreational vehicles, which often incorporate diesel engines having a relatively large oil capacity, but is also useful with diesel engines employed for other applications.
2. Background Art
The use of microprocessors to monitor engine parameters has increased dramatically in recent years due to the development of inexpensive microprocessors coupled with the increase expense of engine fuels and engine structures and components. Sophisticated monitoring systems, such as those shown by U.S. Pat. Nos. 4,053,868 to Cox et al, 4,184,146 to Fratzke et al, 4,258,421 to Juhasc, and 4,344,146 to Panik have been developed to monitor a plurality of engine parameters and to provide an indication or warning of engine conditions. Devices of this type conventionally monitor, among other parameters, oil pressure, oil temperature and oil levels, but normally these monitoring systems measure only existing conditions and perform no predictive functions.
Devices dedicated to providing an accurate measurement of a specific engine parameter have also been developed, as illustrated by the method for measuring engine oil consumption disclosed in U.S. Pat. No. 4,321,056 to Dimitroff. Here, however, consumption is measured by providing additives to the engine lubricant and then analyzing the engine exhaust gas.
Modern diesel engines have relatively large oil capacities, and it is therefore important to accurately monitor the oil consumption of such engines. However, analysis of oil consumption only is not enough and, ideally, a unit dedicated strictly to engine oil monitoring should have a capability to monitor the useful life of engine oil during normal operation of a diesel engine and to indicate to the operator the optimal time to change the oil. A unit having this capability plus the capability of indicating to the operator the oil life which has been used and that which remains would be ideal for effective engine maintenance. However, these indications which involve both actual and predictive functions, are affected by a number of engine variables. It is therefore critical to determine what engine parameters and variables must be measured, and how these measurements must be combined to provide the desired indicating and predictive functions. Oil replacement intervals for a diesel engine can presently be manually calculated using a known formula and chart method for calculating oil change interval, but such calculation involves the use of conditions prevalent at the time of the calculation. If oil is added to the engine or other similar variables occur after a manual calculation, the accuracy of the calculation is adversely affected.